"We block instant messages if they contain malicious or spam URLs based on intelligence algorithms, third-party sources, and/or user complaints. Pirate Bay URLs were flagged by one or more of these and were consequently blocked," explained Microsoft in a statement to The Register.

The Pirate Bay doesn't have a reputation for pushing more malware than any other torrent site, though—but Microsoft has declined to comment further on their banning of the site's URLs. The move signals Microsoft's joining of ranks with an already burgeoning collection of anti-Pirate Bay organizations.